Linux Java HOWTO
maintained by Eric S. Raymond, esr@snark.thyrsus.com
v2.3, 29 May 1996
This document describes how to get started with Java and HotJava under
Linux, as either a user or a programmer.
1. Introduction
This document is a Linux-centric introduction to the world of Java and
HotJava. These technologies are rapidly evolving, and we welcome
contributions from anywhere.
Places in this document that are in serious need of checking or
filling out are bracketed with *** ***. Also see the ``To Be
Added...'' section below. Please help us improve this HOWTO. Send
updates and change requests to .
2. General Questions About Java and HotJava
This section is a general (non-Linux-specific) introduction to Java
and HotJava.
2.1. What are are Java and HotJava and why are they interesting?
Java is a network-aware language superficially resembling C++, but
much smaller and more compact and cleanly designed. It's an
unlimited-extent language with garbage collection like Lisp, but with
static type checking (it's been aptly described as "Smalltalk with
sane syntax"). It includes lightweight processes (threads) as a
native facility and has powerful network-security features. So far,
its major application is the HotJava browser, but it holds
considerable promise as a general-purpose application language.
HotJava is a WWW browser written in Java. Its major advance over most
other browsers is that it knows about a new HTML construct called an
APPLET, which is some Java class that executes on the client machine.
Thus, WWW documents written with Java in mind can have "live" code
objects embedded in them, as opposed to just data.
The ability to safely pass around code objects probably represents the
most significant advance in WWW technology since the first release of
Mosaic. At minimum, it delivers an extensible Web browser that won't
need perpetual upgrading to handle new image formats and tag types.
Java is compiled into a pseudo-code called `J-code'; Java interpeters
execute J-code. J-code may be on its way to becoming a universal
architecture-independent virtual machine-code or compiler intermediate
language. We hear rumors that an ADA-95 compiler that generates J-
code has already been built and that a C compiler is in progress;
eventually, it's likely that multiple front-end languages will be
available for writing either applets or standalone programs on any
machine hosting a Java interpreter.
2.2. Where do Java and HotJava come from? Who can use them?
Java and HotJava were developed at Sun Microsystems by a team headed
by James Gosling (well known as the designer of Gosling Emacs and
NeWS).
The last time Sun tried to set a major technical standard was NeWS,
its Network Window System. Though NeWS was pretty universally
conceded to be technically superior to X, X won because its sources
were freely redistributable. Sun learned from this mistake, and has
made Java/HotJava much more generally available; the sources can be
downloaded under a fairly relaxed license (see ``Java as Freely
Redistributable Software''). Sun is encouraging ports to non-Sun
environments.
Netscape now interprets Java. Microsoft licensed the technology in
early December 1995. So it appears that Java support will probably
become universal in 1996.
Java used to be called Oak. HotJava was once known as WebRunner.
2.3. How mature is Java?
On December 12 1995 Sun released the `Beta 2' version of Java. A
month later it released 1.0, the first `production' version. The Java
environment API defining its access to the host OS and windowing
system has allegedly been semi-frozen -- it may be extended, but won't
be incompatibly changed.
The 1.0 version of this FAQ was issued along with the beta 1.0 Java
Developer's Kit (JDK) for Linux, ported by Randy Chapman.
Significant holes are known to exist in the Java security
implementation. It is not yet a good idea to use Java for sensitive
applications. These problems are expected to be fixed in the
production (post-beta) releases.
2.4. Where can I find documentation on Java and HotJava?
Sun maintains an extensive HTML web of Java and HotJava-related
documents at . These documents are mirrored at
and elsewhere; see Sun's list of mirror
sites.
2.5. Yes, but where can I find paper documentation?
SunSoft Press's official series of Java books is in the production
pipeline at Addison-Wesley. Some details about these can be found in
the comp.lang.java FAQ .
Several Java early-adopters have recommended "Hooked on Java" by the
members of the Java team. "Well written, though I'd appreciate
something less basic" was one comment.
O'Reilly Associates is working on its own series of Java books in
cooperation with Sun. Your humble editor is the primary technical
reviewer for this series. So far (as of May 1996), only the "Java In
a Nutshell" guide has come out; it's pretty good. The series will
include (at least) a language reference, a class library reference,
and a book on the underlying byte-code virtual machine.
SAMS has a book called "Learning Java in 21 Days". No review yet.
One of our contributors, browsing his local Bookstop/Barnes &
Noble/Borders, came up with 3 books already out:
· One called 'Java in 60 minutes' that looked like a pretty strict
syntactic description (about $20).
· One from SamsNet called just `Java' (about $20).
· One by Tim Ritchey called `Java!' that includes a CD-ROM (about
$35).
Our informant continues: "I bought the 3rd one (by Tim Ritchey).
Paper leadtimes being what they are, the CD-ROM only has alpha
stuff, though it mentions that the beta version might be out by the
time you read it and suggests java.sun.com as a place to get more
recent information. Other than that, it's pretty good, even to
pointing out that `well, it's pointless for me to spam you with
pages and pages of API descriptions because 1) it would quadruple
the size of the book and 20 they're still ch anging and 2) you can
get that info online at ...etc'"
Dave Dittrich writes: I'd say that "Java in 60 minutes" may take you
60 minutes to read, but won't teach you how to program in Java in 60
minutes (surprise, surprise!) It looks to me like "Java in 60
minutes" is one of the many attempts be first to market with a book on
a hot topic. It didn't seem to include much more than you can find
right now on the Web, including lots of text that looks like it was
lifted straight out of the Java Language Specification
(http://java.sun.com/JDK-beta2/psfiles/javaspec.ps).
Dave continues: Same thing with "Java!", only the latter goes into
much more detail on object oriented programming concepts, etc.
Someone pointed me to another text book that is equally as good at
covering data/method abstraction and other object oriented programming
concepts, which is "Structure and Interpretation of Computer Programs"
by Abelson, Sussman and Sussman (MIT Press).
Final caveat: at this point (January 1996), it is probly a good idea
to stay away from the Ritchey book or anything else based on the alpha
API. The beta API is substantially different, and the soon-to-be-
released Java 1.0 will have its own differences.
2.6. Where can I find on-line collections of Java code?
WWW archives of applets are available at the following locations:
·
·
·
·
Most of the applets on these pages come with source code, and
programmers are invited to use them.
Pointers to others may be available in the comp.lang.java FAQ
.
3. Java as Freely Redistributable Software
Many Linux programmers are attached to producing freely
redistributable software (FRS), and try to avoid committing a lot of
time to tools for which sources are not generally available. In this
section, we discuss Sun's and Java's relationship with the FRS world.
(Warning: I am not a lawyer. I am neither employed by, nor an agent
of, nor a stockholder in, Sun Microsystems. This section is based on
my interpretation of the current copyright law and the Sun licensing
language. Treat this as an introduction; the Sun licensing page,
is definitive. If you
are in serious doubt about what it means, consult an attorney.)
3.1. Are Java programs and applets freely redistributable?
They are if you write them and choose to make them FRS through some
mechanism (such as the GPL, or a BSD-style license, or declaring them
public domain).
3.2. What can I do with Java implementation binaries?
The Sun licensing page has this to say:
The unmodified Java and HotJava binary releases may be
redistributed free of charge in both commercial and non-
commercial applications.
Also:
Companies or individuals who wish to create a new port of
the Java language have the right under this agreement to
post the binaries of that port to the Internet for use by
others, as long as the port is free of charge and passes the
publicly available test suites. (Test suites will be avail­
able sometime in the first half of 1996.) The "diffs" may
also be posted on the web as long as the underlying source
code is not posted. The Java source code is
So if you've got a working Java or HotJava binary, you can give it to
your buddies. Or put it on a CD-ROM. Or do anything except patch it
and represent the patched version as Java. (This is reasonable. Sun
obviously can't leave itself without recourse against Trojan horses
sailing under the Java banner.) Binaries are FRS.
3.3. Which parts of the Java sources are freely redistributable?
According to Sun's licensing page, none of it is. But that sounds
harsher than it is. In practice, anyone can get the Java and HotJava
sources for educational, porting, and non-commercial purposes by
filling out a Web form which obligates them not to redistribute the
sources. And the agreement does permit redistribution of diffs
against the sources.
The only circumstance that requires you to sign a commercial license
with Sun and pay them money is if you want to use the sources in a
commercial product. In particular, the way the language is written,
it's within the letter and spirit of the agreement for you to sign
Sun's noncommercial source license, snarf the source, port it, and
give away the resulting binaries as completely unencumbered freeware!
Sun says that its primary purpose in keeping as much control as it has
is to keep the language from mutating into incompatible dialects. The
license language supports this; it seems to have been designed to
allow hackers to play for free.
3.4. What is Sun's attitude towards FRS Java implementations and
tools?
The Sun licensing page says:
The specifications for the Java Language and the Java Vir­
tual Machine are OPEN and are copyrighted by Sun Microsys­
tems, Inc.
Reimplementations of the Java Compiler or the Java Runtime
Interpreter are permitted without requiring a license from
Sun provided such implementations are created directly from
the published specifications and without the direct or indi­
rect use of Sun's own implementations or other intellectual
property rights, including trademarks.
So if you want to go to the effort of creating a Java clone from the
published specifications that is FRS, Sun won't stop you.
Sun people use the term "rogue port" for Java implementations that
either (a) are performed outside Sun, or (b) don't rely on Sun-
licensed code (sometimes the term seems to mean one thing, sometimes
the other). They seem to think some of these already exist, but we
don't know where they are, nor if they are FRS. They're pretty
relaxed about the situation.
Sun has a Java validation suite. They have said they'll certify any
Java port that passes it. (Whether this validation will cost money is
unknown, but Sun says in writing that the suite wil be "publicly
available" in 1996, which at least hints that it will not.) They're
prepared to certify rogue ports, though this apparently hasn't
happened yet.
3.5. Is anyone cloning Java in freely redistributable source?
There is a clone of the Java compiler in early development. It's
called guavac. You can find more information at
There is a free runtime Java system called Kaffe. You can find more
information at .
There's a FAQ at
.
There was a rumor afloat that Cygnus Software's GROW project has plans
for a Java byte code interpreter to be issued under GPL. This is
false; what they are working on is a Java-to-native-code compiler that
doesn't go through J-code. You can get more information on related
efforts at
.
Per Bothner of Cygnus has written free replacements (more-or-less) for
javah and javap. (See ftp.cygnus.com:pub/bothner/gjava*.tar.gz.)
Erik Troan of Red Hat and your humble editor are attempting to put
together a development group to do the rest of the job. Right now it
looks like we'll use guavac as the compiler, Erik will do the class
library and your humble editor will do the byte-code interpreter (if
Cygnus hasn't gotten there first). This project was tentatively named
"Mr. Coffee" but is now called JOLT (Java Open Library & Tools).
3.6. Are there any FRS Java Tools?
There is a GNU Emacs mode for editing Java. You can fetch it from
. Note: this mode assumes
you're using c++-mode.el, and won't work with the cc-mode.el
distributed with Emacs 19.
4. Java On Linux Questions
Here you can learn the nuts and bolts of getting Java running on your
Linux.
4.1. Are Java and HotJava included in any of the Linux distributions?
No, not yet, but expect it any week now.
4.2. How can I get the latest Java distribution for Linux?
Look in . There is a list
of mirror sites you can download it from.
The files you'll need are linux.jdk-1.0-try1.common.tar.gz and one of
either linux.jdk-1.0-try3.static-motif-bin.tar.gz or
linux.jdk-1.0-try3.shared-motif-bin.tar.gz, depending on whether you
have Motif shared libraries on your system.
If you have Red Hat Linux or some other system that speaks RPM, you
can install the 1.0 beta from
and
or
.
For European users, the contents of
ftp://java.blackdown.org/pub/Java/linux and
ftp://java.blackdown.org/pub/Linux/RPMS/i386/JDK-linux* are now
mirrored in the UK in .
That's zen.btc.uwe.ac.uk, in case anyone cares. Mirroring happens
daily at about 6am UK time.
This port (from the Sun sources by Randy Chapman) is the one that's
referred to (as the JDK) elsewhere in this HOWTO.
4.3. What environment will I need to run Java?
For starters, you need an ELF-based Linux. There is no a.out support,
and at the speed the Linux world is switching over to ELF there is not
likely to be any in the future.
You need a 1.2.13 or later kernel. Kernels 1.2.12 and older seem to
have a bug in getcwd(3) that tanks bin/javac because it doesn't check
the getcwd(3) return code.
You'll need these pieces:
· libc.so.5 => /lib/libc.so.5.2.18
· libX11.so.6 => /usr/X11/lib/libX11.so.6.0
· libXt.so.6 => /usr/X11/lib/libXt.so.6.0
· libXext.so.6 => /usr/X11/lib/libXext.so.6.0
· libXpm.so.4 => /usr/X11/lib/libXpm.so.4.3
· libdl.so.1 => /lib/libdl.so.1.7.9
The C and X support libraries may be in your Linux already.
If you don't already have it, get libc.5.2.18.bin.tar.gz from
. Uncompress and untar
and copy the files in the lib subdirectory of the top level of the
hierarchy to /lib.
If you don't have a current version of ld.so (or libdl.so.1.7.*) you
will need to update. ld.so.1.7.9 and .11 will work; .10 and other
early versions will not. Get ld-so.1.7.14.tar.gz from
; Uncompress and untar it and run
instldso.sh which is in the top level of the resulting hierarchy.
You can get an Xpm library that will work from
.
4.4. Do I need Netscape? Can I use Netscape?
Yes, you need Netscape. HotJava isn't yet available for the beta pr
1.0 releases. Randy Chapman says:
Sun massively changed the awt interface when they shipped
the beta JDK and have not yet converted HotJava to it. They
have promised they will, and it should work great with
linux-jdk when they release it.
It's unknown when this will happen.
Netscape versions starting from 2.0b3 are Java-aware. It is available
at ftp1-7.netscape.com (i.e. at ftp1.netscape.com,
ftp2.netscape.com,... etc.) Version 2.0b4 and up will allow you to
read applets from file: URLs, 2.0b3 didn't. This should be a big help
for folks with small-memory machines (they don't need an httpd
running).
Note that Netscape will run on an a.out system, so it is, in theory,
possible to write your java app, give it to someone else to compile
(like maybe the BlackStar Public Compiler
), and see the output on your system. If
you want more than that, get an ELF system.
Make sure CLASSPATH is not set before running netscape; having it set
seems to crash Netscape, and if you follow the directions below it
won't need tweaking.
The Linux Netscape port has a few known problems. It doesn't do
sound. Only 8-bit displays work; 16bpp displays yield crashes. The
2.0b3 version occasionally yields bus errors when caling the dispose
method for frames. While it's pretty robust otherwise, Gamelan's
`Impressionism' applet is known to crash it.
4.5. What mailing lists or newsgroups exist for supporting Java on
Linux?
· java-linux (Maintained by karl@blackdown.org) Discussions and
developments concerning the port of Java to the Linux operating
system. Email to java-linux-request@java.blackdown.org with the
word `subscribe' in the subject to be added to the list.
· java-linux-announce (Maintained by karl@blackdown.org) Moderated
list for announcements concerning the Java-Linux porting projects.
Please send e-mail to java-linux-announce-
request@java.blackdown.org with the word subscribe in the subject,
to be added to the list.
· comp.lang.java Newsgroup for general Java discussion.
· alt.www.hotjava Newsgroup for discussion of the HotJava browser.
5. Building the Linux Java port on stock Linuxes
In this section, we collect recipes sent to us for building Randy
Chapman's Java port on various current Linux distributions:
5.1. Slackware distribution ELF kernel 1.2.13.
John Franks writes that he succeeded with the
following steps:
· Get linux-x86.jdk.static-motif.tar.gz from
and uncompress it and
untar it. (The filenames you must fetch have changes for the 1.0
beta JDK.)
· Get libc.5.2.18.bin.tar.gz (binary distribution, not source) from
Uncompress and untar
and copy the files in the lib subdirectory of the top level of the
hierarchy to /lib. Make sure that /lib/libc.so.5 is a symlink to
this file.
· Get ld-so.1.7.14.tar.gz from ftp://ftp.ods.com/linux/ Uncompress
and untar it and run "instldso.sh" which is in the top level of the
resulting hierarchy.
You should now be able to compile and try the "hello world" program
and applet from Sun following the instructions at
.
5.2. RedHat 2.1/Caldera Preview 2
Steve Greene reports success doing the
following steps. I have edited the recipe slightly, so blame any
mistakes on me. The `JDK' he refers to is the Chapman port of the
Java Developer's Kit.
· From a Red Hat mirror site, get the rpm available for ld.so.1.7.14.
To find it, check any RedHat mirror site for:
/pub/mirrors/redhat-2.1/updates/RPMS/ld.so-1.7.14-i386.rpm
I know it is available at ftp.pht.com, ftp.caldera.com. and is
probably at the other RedHat mirrors as well. Grab it, and do `rpm
-Uvh ld.so-1.7.14-1.i386.rpm' on your system.
· Red Hat 2.0 and Caldera Preview 2 users may need the `which'
program (it's called by some of the scripts in the JDK). An rpm
file for `which' is available at the usual Red Hat mirror sites as
part of the Red Hat 2.1 distribution files. Get and install
which-1.0.i386.rpm. RedHat 2.1 users should already have which on
their system or available within their original distribution.
· Get the tar file(s) for the statically-linked JDK. Untar it from a
convenient point. I put mine in /usr/local, so the untar creates
/usr/local/java/....
· So you can run java as someone other than root (this is a good
idea!), do `chmod 666 /dev/zero'. Red Hat and Caldera have the
wrong permissions set on this device out of the box.
· If you haven't already, run ldconfig as root to load the new
libraries. If you do "ldconfig -v" you can verify you have all
the libraries loaded. (At least we don't have to build an ELF
system first!)
· Make sure you're logged in as a user (e.g. non-root). Start X-
windows, open an X-Term, and try something!
5.3. Unifix
Stefan Middendorf writes: Unifix is a popular German-language Linux
distribution. There are a few distributions based on it: Linux
Universe, sold in USA, Linux 4U, currently only distributed in Germany
and Linux FT in Britain. This recipe is known to work for Unifix 1.7,
Linux 4U 1st Edition, Linux Universe 2nd Edition, and Linux FT 1.1.
· Put linux-x86.jdk.static-motif.tar.gz from
in /usr/local and
uncompress it and untar it.
· Change the first line of the script .java_wrapper from PRG=`which
$0` >/dev/null 2>&1 to
PRG=`type $0 | cut -d ' ' -f 3` >/dev/null 2>&1
· Get libc-5.2.18.bin.tar.gz (I succeeded with
libc-5.2.16.bin.tar.gz, too), extract and uncompress it in the /
drectory.
· Get ld-so.1.7.12.tar.gz from tsx-11.mit.edu (or any mirror site)
and uncompress and untar it, e.g. in /usr/local. Change to the
resulting directory and run instldso.sh. This will also run
ldconfig. Probably newer versions of ld-so will work too.
· Add /usr/local/java/bin to the PATH environment variable.
· Get netscape-v20b4-export.i486-unknown-linux.tar.Z, extract and
uncompress it in /usr/local/.
· Create a Link in /usr/local/bin to ..//netscape.
· Put /usr/local//moz2_0.zip in
/usr/local/lib/netscape/.
As an alternative to changing your PATH, Ralf Strobel suggests:
· Copy the scripts .java_wrapper and appletviewer and the links @java
@javac, @javadoc, @javap, and @jdb from /usr/local/java/bin to
/usr/local/bin and you can use them wherever you are.
· In /java/bin/i586 you can add a script called `javadoc`
#!/bin/sh `dirname $0`/java sun.tools.javadoc.Main -d
$*
where if you are user jrandom, would be
jrandom/.java-html.
6. Viewing Applets
To run a demo without going through the applet viewer, you can enter
this command from the top of my Java directory tree (/usr/local/java
on most systems):
bin/java sun.applet.AppletViewer demo//exampleN.html
where is the subdirectory off demo, and N is the
number of the example file (some directories have more than one).
Steve Greene says: I've started the tutorials available from Sun's
java site and the similar one put out by the NTMUG. I've discovered
some problems with the syntax in Sun's tutorial, so I've been
following the NYMUG tutorial instead for now.
The appletviewer expects as an argument, an html file with an APPLET
tag inside it.
For example, if your html file Hello.html looks like:
Hello test program
< /HEAD>
This is an appletviewer test